South West Main Line

The Southampton and Dorchester Railway was also formed and built a line from 1845 to 1847 from Southampton to Dorchester. It avoided Bournemouth, then barely a village, and ran via Ringwood and Wimborne Minster before reaching Dorchester. It took a winding route, which followed the easiest-to-construct links rather than linking settlements in a straight line. In particular, due to intervention by the Commissioners of Woods and Forests, the route between Southampton and Ringwood had to take a southward diversion through Brockenhurst, rather than the straight route through Lyndhurst that the company had envisioned.[4] The line also bypassed Poole. Initially, Poole was served by a branch from Hamworthy (initially named Poole Junction) to a station on the opposite side of Holes Bay.

The Ringwood line was nicknamed as 'Castleman's Corkscrew' after Charles Castleman, a major figure in the enterprise.[5] The line was originally planned to continue towards Exeter, but this never came into effect. In 1865 the railway was connected to the GWR line to Weymouth, which now forms the current terminus of the line.

A branch was built in the 1870s from Broadstone to central Poole that continued eastwards to Bournemouth, a town that was now developing as a seaside resort. From 1886 to 1888, a line was then built from Brockenhurst to Bournemouth. A causeway was also built across Holes Bay to connect Poole to Hamworthy. In time, the straighter route through Bournemouth and Poole superseded the Ringwood line. The Ringwood line was closed by the Beeching Axe.

The L&SWR's biggest rival was the Great Western Railway (GWR) who had originally cut the L&SWR's plans by building the line to Bristol. Both companies built several railways from their own networks into each other's intended territory.

In 1848, the GWR built a branch from Reading to Basingstoke. At first this was a fairly quiet railway with a terminus separate from the L&SWR's mainline station. However, when the rival company adopted standard gauge, a link was constructed between the two lines. This later became used for a freight route from Southampton to the Midlands via Oxford. Following the closure of the Somerset and Dorset Joint Railway, this route became used by long-distance services from Bournemouth to the Midlands.

Another line was built in 1873 southward (Didcot, Newbury and Southampton Railway). Originally, L&SWR ruled out allowing the line to use its own track. However the DN&SR fell into financial difficulties, and negotiations allowed its trains to use the South West Main Line south of Winchester.

GWR also proposed building a line from Reading to Portsmouth via Basingstoke and Alton but L&SWR found a cheaper solution for building the northern stretch from Basingstoke to Alton by using a light railway. The Basingstoke and Alton Light Railway stopped a rival's Portsmouth line from being built at the all-too-common cost of being, for most of its existence, unprofitable - it saw an eight-year resurrection but again became loss-making and closed in 1932 save for goods. In 1955 similarly the southern stretch, the Meon Valley Railway, closed to passengers.

Between London Waterloo and Clapham Junction, the line has eight tracks. It runs over the Nine Elms to Waterloo Viaduct for much of its length. It crosses beneath the Chatham Main Line where the Brighton Main Line runs alongside it on the southern side. At Clapham Junction, some of these tracks leave on the Waterloo to Reading Line and the remaining tracks are reduced to four. The Brighton Line, which also has four tracks, separates from it shortly afterwards.

The four tracks initially have a pair of "slow" tracks to the east with the two "fast" tracks on the western side. This arrangement continues to north of Wimbledon where a flyover transfers the northbound slow line across the fast lines, leaving the inner tracks being used for the fast services and the stopping services using the outer tracks. This arrangement continues to Worting Junction, just after Basingstoke. Many stations on this section had island platforms which have since been removed - this is evident with wide gaps between station platforms at stations such as Winchfield. The island platforms survive at New Malden, Esher and Walton-on-Thames, although mothballed and out of use.

The line continues as double-track to Winchester but expands to three tracks through Shawford station with one up platform and fast and slow down platforms. There are four tracks from Shawford to Eastleigh. The line from Romsey via Chandler's Ford trails in just north of Eastleigh which is also the junction for the Fareham line. The line returns to double track until St Denys where the West Coastway Line trails in. At Northam the original route to Southampton Terminus carries on south towards Eastern Docks and the main route curves west to enter a tunnel through to Southampton Central station.

The line remains double-tracked most of the way to Weymouth, but there is a single-track section between Moreton and Dorchester South which constrains capacity.[6]

The 'Surrey section', about half of which has become Greater London, was electrified, as far west as Pirbright Junction (for Alton) using the (750 V DC third rail) system, by the London & South Western Railway or its successor, the Southern Railway before World War II.

The bulk of the line (that is from Pirbright Junction to Bournemouth/Bournemouth Depot) was electrified in 1967. From then until 1988 trains on the Bournemouth to Weymouth section operated a push-pull system. One or two BR Class 438 4-TC units would be propelled from London to Bournemouth by a BR Class 432 4-REP unit, controlled from the leading cab of the former. At Bournemouth, one or both of the Class 438 4-TCs would continue over the unelectrified line to Weymouth hauled by a BR Class 33/1 diesel locomotive. Trains from Weymouth would follow the same procedure in reverse.

Electrification was extended to Weymouth in 1988 and saw the introduction of then new Class 442 Wessex Electric trains. These were withdrawn by February 2007; Class 444 and Class 450 trains are now used.

• Butt, R.V.J. (1995). The Directory of Railway Stations. Patrick Stephens Ltd. ISBN 1-85260-508-1.
• Lucking, J.H. (1968). Railways of Dorset. Railway Correspondence and Travel Society.
• Mitchell, Vic; Smith, Keith (1992). Branch Lines Around Wimborne. Middleton Press. ISBN 0-906520-97-5.